Lorena Escudero (IFIC, Valencia) on behalf of the T2K collaboration

Understanding Neutrinos 20124<strong>Lorena</strong> <strong>Escudero</strong>The Far Detector: SKMuon neutrino event(νμ μ clear single ring)Electron neutrino event(νe e EM shower, fuzzy ring)22.5kton water Cherenkovdetector.Cherenkov photons reach PMTsand produce ring-shaped hit patternMC eventMC event

Understanding Neutrinos 20125<strong>Lorena</strong> <strong>Escudero</strong>The Near Detectors I:INGRID(ON Axis)INGRID (Interactive Neutrino GRID) monitors directly theneutrino beam direction and intensity by means of neutrinointeractions in iron.Each INGRID module is composed of iron plates +scintillator layers in a sandwich.

The Near Detectors II:ND280(OFF Axis)ND280 goal is to measure the flux, energyspectrum and νe contamination.Cross section studies are also performed.ECALElectromagnetic calorimeters (plasticscintillator).Understanding Neutrinos 20126<strong>Lorena</strong> <strong>Escudero</strong>

The Near Detectors II:ND280(OFF Axis)ND280 goal is to measure the flux, energyspectrum and νe contamination.Cross section studies are also performed.ECALElectromagnetic calorimeters (plasticscintillator).ND280 Magnet & SMRDOld CERN UA1/NOMAD magnet (0.2T)MUON detector (SMRD): scintillatorinserted in magnet air gapsUnderstanding Neutrinos 20126<strong>Lorena</strong> <strong>Escudero</strong>

The Near Detectors II:ND280(OFF Axis)ND280 goal is to measure the flux, energyspectrum and νe contamination.Cross section studies are also performed.ECALElectromagnetic calorimeters (plasticscintillator).ND280 Magnet & SMRDOld CERN UA1/NOMAD magnet (0.2T)MUON detector (SMRD): scintillatorinserted in magnet air gapsPi 0 detector (P∅D)Scintillator + water detector.Optimized for γ detection and π0reconstruction (neutrino NC process).Understanding Neutrinos 20126<strong>Lorena</strong> <strong>Escudero</strong>

The Near Detectors II:ND280(OFF Axis)ND280 goal is to measure the flux, energyspectrum and νe contamination.Cross section studies are also performed.ECALElectromagnetic calorimeters (plasticscintillator).TRACKER3 Time Projection Chambers (TPCs)- They reconstruct momentum and chargeof particles.2 Fine Grained Detectors (FGDs)- Active target for neutrino interactions:carbon + water.ND280 Magnet & SMRDOld CERN UA1/NOMAD magnet (0.2T)MUON detector (SMRD): scintillatorinserted in magnet air gapsPi 0 detector (P∅D)Scintillator + water detector.Optimized for γ detection and π0reconstruction (neutrino NC process).Understanding Neutrinos 20126<strong>Lorena</strong> <strong>Escudero</strong>

The Near Detectors II:ND280(OFF Axis)ND280 goal is to measure the flux, energyspectrum and νe contamination.Cross section studies are also performed.ECALElectromagnetic calorimeters (plasticscintillator).TRACKER3 Time Projection Chambers (TPCs)- They reconstruct momentum and chargeof particles.2 Fine Grained Detectors (FGDs)- Active target for neutrino interactions:carbon + water.ND280 Magnet & SMRDOld CERN UA1/NOMAD magnet (0.2T)MUON detector (SMRD): scintillatorinserted in magnet air gapsPi 0 detector (P∅D)Scintillator + water detector.Optimized for γ detection and π0reconstruction (neutrino NC process).Understanding Neutrinos 20126<strong>Lorena</strong> <strong>Escudero</strong>

The Near Detectors II:ND280(OFF Axis)ND280 goal is to measure the flux, energyspectrum and νe contamination.Cross section studies are also performed.ECALElectromagnetic calorimeters (plasticscintillator).TRACKER3 Time Projection Chambers (TPCs)- They reconstruct momentum and chargeof particles.2 Fine Grained Detectors (FGDs)- Active target for neutrino interactions:carbon + water.ND280 Magnet & SMRDOld CERN UA1/NOMAD magnet (0.2T)MUON detector (SMRD): scintillatorinserted in magnet air gapsPi 0 detector (P∅D)Scintillator + water detector.Optimized for γ detection and π0reconstruction (neutrino NC process).Understanding Neutrinos 20126<strong>Lorena</strong> <strong>Escudero</strong>

Understanding Neutrinos 20127<strong>Lorena</strong> <strong>Escudero</strong>Oscillation Analysis Method

Understanding Neutrinos 20127<strong>Lorena</strong> <strong>Escudero</strong>Oscillation Analysis MethodFlux prediction• Beam MC• Hadron production (NA61)ND280 analysis• Detector MC• νμ measurements in CC QEand nonQE samplesν cross sections• NEUT MC model• Uncertainties set fromexternal data

Understanding Neutrinos 20127<strong>Lorena</strong> <strong>Escudero</strong>Oscillation Analysis MethodFlux prediction• Beam MC• Hadron production (NA61)ND280 analysis• Detector MC• νμ measurements in CC QEand nonQE samplesν cross sections• NEUT MC model• Uncertainties set fromexternal dataFlux+cross section FITTo constrain flux and ν interactioncross section uncertaintiesnear detectoruncertainties

Understanding Neutrinos 20127<strong>Lorena</strong> <strong>Escudero</strong>Oscillation Analysis MethodFlux prediction• Beam MC• Hadron production (NA61)ND280 analysis• Detector MC• νμ measurements in CC QEand nonQE samplesν cross sections• NEUT MC model• Uncertainties set fromexternal dataFlux+cross section FITTo constrain flux and ν interactioncross section uncertaintiesnear detectoruncertaintiesFar detector analysis

Understanding Neutrinos 20127<strong>Lorena</strong> <strong>Escudero</strong>Oscillation Analysis MethodFlux prediction• Beam MC• Hadron production (NA61)ND280 analysis• Detector MC• νμ measurements in CC QEand nonQE samplesν cross sections• NEUT MC model• Uncertainties set fromexternal dataFlux+cross section FITTo constrain flux and ν interactioncross section uncertaintiesnear detectoruncertaintiesFar detector analysisMC Prediction• SK detector MC• Calculate prediction (eventrates, spectra) at different osc.hypothesesExtrapolationPropagate using data/MC ratioand near/far flux transfer matrix

Understanding Neutrinos 20127<strong>Lorena</strong> <strong>Escudero</strong>Oscillation Analysis MethodFlux prediction• Beam MC• Hadron production (NA61)ND280 analysis• Detector MC• νμ measurements in CC QEand nonQE samplesν cross sections• NEUT MC model• Uncertainties set fromexternal dataFlux+cross section FITTo constrain flux and ν interactioncross section uncertaintiesnear detectoruncertaintiesFar detector analysisMC Prediction• SK detector MC• Calculate prediction (eventrates, spectra) at different osc.hypothesesData•T2K event candidatesExtrapolationPropagate using data/MC ratioand near/far flux transfer matrix

Understanding Neutrinos 20127<strong>Lorena</strong> <strong>Escudero</strong>Oscillation Analysis MethodFlux prediction• Beam MC• Hadron production (NA61)ND280 analysis• Detector MC• νμ measurements in CC QEand nonQE samplesν cross sections• NEUT MC model• Uncertainties set fromexternal dataFlux+cross section FITTo constrain flux and ν interactioncross section uncertaintiesnear detectoruncertaintiesFar detector analysisMC Prediction• SK detector MC• Calculate prediction (eventrates, spectra) at different osc.hypothesesData•T2K event candidatesExtrapolationPropagate using data/MC ratioand near/far flux transfer matrixOscillation FITCompare data andexpectations to extractthe values of theoscillation parametersotheruncertainties

2010 νμ Disappearance Analysis: SELECTIONRUN1+2 = 1.43 E20 POTAt the far detector a νμ CCQEenriched sample is selected.CUTEVENTS (DATA)FCFV (+beam timing) 88Single Ring 41PID (μ-like) 33pμ > 200MeV 33< 2 decay e - 31Understanding Neutrinos 20128<strong>Lorena</strong> <strong>Escudero</strong>

2010 νμ Disappearance Analysis: SELECTIONRUN1+2 = 1.43 E20 POTAt the far detector a νμ CCQEenriched sample is selected.CUTEVENTS (DATA)FCFV (+beam timing) 88Single Ring 41PID (μ-like) 33pμ > 200MeV 33< 2 decay e - 31Understanding Neutrinos 20128<strong>Lorena</strong> <strong>Escudero</strong>

2010 νμ Disappearance Analysis: SELECTIONRUN1+2 = 1.43 E20 POTAt the far detector a νμ CCQEenriched sample is selected.CUTEVENTS (DATA)FCFV (+beam timing) 88Single Ring 41PID (μ-like) 33pμ > 200MeV 33< 2 decay e - 31Understanding Neutrinos 20128<strong>Lorena</strong> <strong>Escudero</strong>

2010 νμ Disappearance Analysis: SELECTIONRUN1+2 = 1.43 E20 POTAt the far detector a νμ CCQEenriched sample is selected.CUTEVENTS (DATA)FCFV (+beam timing) 88Single Ring 41PID (μ-like) 33pμ > 200MeV 33< 2 decay e - 31Understanding Neutrinos 20128Based on shape of ring<strong>Lorena</strong> <strong>Escudero</strong>

2010 νμ Disappearance Analysis: SELECTIONRUN1+2 = 1.43 E20 POTAt the far detector a νμ CCQEenriched sample is selected.CUTEVENTS (DATA)FCFV (+beam timing) 88Single Ring 41PID (μ-like) 33pμ > 200MeV 33< 2 decay e - 31Understanding Neutrinos 20128Based on shape of ring<strong>Lorena</strong> <strong>Escudero</strong>

2010 νμ Disappearance Analysis: SELECTIONRUN1+2 = 1.43 E20 POTAt the far detector a νμ CCQEenriched sample is selected.CUTEVENTS (DATA)FCFV (+beam timing) 88Single Ring 41PID (μ-like) 33pμ > 200MeV 33< 2 decay e - 31Understanding Neutrinos 20128Based on shape of ring<strong>Lorena</strong> <strong>Escudero</strong>

2010 νμ Disappearance Analysis: SELECTIONRUN1+2 = 1.43 E20 POTAt the far detector a νμ CCQEenriched sample is selected.CUTEVENTS (DATA)FCFV (+beam timing) 88Single Ring 41PID (μ-like) 33pμ > 200MeV 33< 2 decay e - 31Last two vetoes rejectevents with unseenmuons and pionsUnderstanding Neutrinos 20128Based on shape of ring<strong>Lorena</strong> <strong>Escudero</strong>

Understanding Neutrinos 20129<strong>Lorena</strong> <strong>Escudero</strong>2010 νμ Disappearance Analysis: RESULTS90% CLEVENTS EXPECTED• No oscillation: 106(No oscillation excluded at 4.5σ)• Maximal oscillation (sin 2 (2θ23)=1,Δm 2 23 = 2.4E-3eV 2 ): 28.3EVENTS OBSERVED: 31• Two independent analyses done, withconsistent results• Results in full agreement withMINOS, SK

Understanding Neutrinos 201210<strong>Lorena</strong> <strong>Escudero</strong>2012 νe Appearance Analysis: SELECTIONRUN1+2+3 = 3E20 POTCUTEVENTS (DATA)FCFV (+beam timing) 174Single Ring 88PID (e-like) 22Evis > 100MeV 21No decay e - 16Inv. mass cut 11Eν rec

Understanding Neutrinos 201210<strong>Lorena</strong> <strong>Escudero</strong>2012 νe Appearance Analysis: SELECTIONRUN1+2+3 = 3E20 POTCUTEVENTS (DATA)FCFV (+beam timing) 174Single Ring 88PID (e-like) 22Evis > 100MeV 21No decay e - 16Inv. mass cut 11Eν rec

Understanding Neutrinos 201210<strong>Lorena</strong> <strong>Escudero</strong>2012 νe Appearance Analysis: SELECTIONRUN1+2+3 = 3E20 POTCUTEVENTS (DATA)FCFV (+beam timing) 174Single Ring 88PID (e-like) 22Evis > 100MeV 21No decay e - 16Inv. mass cut 11Eν rec

Understanding Neutrinos 201210<strong>Lorena</strong> <strong>Escudero</strong>2012 νe Appearance Analysis: SELECTIONRUN1+2+3 = 3E20 POTCUTEVENTS (DATA)FCFV (+beam timing) 174Single Ring 88PID (e-like) 22Evis > 100MeV 21No decay e - 16Inv. mass cut 11Eν rec

Understanding Neutrinos 201210<strong>Lorena</strong> <strong>Escudero</strong>2012 νe Appearance Analysis: SELECTIONRUN1+2+3 = 3E20 POTCUTEVENTS (DATA)FCFV (+beam timing) 174Single Ring 88PID (e-like) 22Evis > 100MeV 21No decay e - 16Inv. mass cut 11Eν rec

2012 νe Appearance Analysis: SELECTIONRUN1+2+3 = 3E20 POTCUTEVENTS (DATA)FCFV (+beam timing) 174Single Ring 88PID (e-like) 22Evis > 100MeV 21No decay e - 16Inv. mass cut 11Eν rec

2012 νe Appearance Analysis: SELECTIONRUN1+2+3 = 3E20 POTCUTEVENTS (DATA)FCFV (+beam timing) 174Single Ring 88PID (e-like) 22Evis > 100MeV 21No decay e - 16Inv. mass cut 11Eν rec

2012 νe Appearance Analysis: SELECTIONRUN1+2+3 = 3E20 POTCUTEVENTS (DATA)FCFV (+beam timing) 174Single Ring 88PID (e-like) 22Evis > 100MeV 21No decay e - 16Inv. mass cut 11Eν rec

2012 νe Appearance Analysis: SELECTIONRUN1+2+3 = 3E20 POTCUTEVENTS (DATA)FCFV (+beam timing) 174Single Ring 88PID (e-like) 22Evis > 100MeV 21No decay e - 16Inv. mass cut 11Eν rec

Understanding Neutrinos 201211<strong>Lorena</strong> <strong>Escudero</strong>2012 νe Appearance Analysis: RESULTSBEST FIT(with 68% CL error, @δCP=0)• Normal hierarchy• Inverted hierarchy

Conclusions / Future PlansT2K has been taking data since 2010.We are reporting evidence of νe appearance. Latestresult, based on 3E20 POT, recently reported (ICHEP 2012).θ13 values compatible with reactor experiments.Updated results on νμ disappearance coming soon.Current θ23, Δm 2 23 values compatible with MINOS, SKSummer 2012 shutdown underway.Data taking will be restarted in October 2012Planned to take more data at higher beam powerUnderstanding Neutrinos 201212<strong>Lorena</strong> <strong>Escudero</strong>

Thanks for your attention!REFERENCES[1] The T2K ExperimentNIMA, DOI number: 10.1016/j.nima.2011.06.067 (2011) arXiv:1106.1238[2] Indication of Electron Neutrino Appearance from anAccelerator-Produced Off-axis Muon Neutrino Beam:Phys. Rev. Lett. 107, 041801 (2011)[3] First muon-neutrino disappearance study with an off-axisbeamPhys. Rev. D 85, 031103(R) (2012) arXiv:1201.1386

BACKUP

Some Neutrino PhysicsNEUTRINO MIXINGMatrix connecting mass and flavor eigenstates (PMNS)6 independent parameters describing oscillations: 3 angles, 2 masssplitting parameters and one phase:Solar parameters(very well known)θ12, Δm 2 12Atmospheric parameters(well known)θ23, Δm 2 2315Interferenceparameters (unknown)θ13, δCP

The T2K Collaboration12 countries61 institutions~500 authorsPublic website:http://t2kexperiment.org/16

The Beam18

19The Off Axis MethodsecondarybeamlineT2K is the first long baseline experiment using the off-axistechnique. The current off-axis angle is 2.5º(2º-2.5º range allowedby the facility design).Characteristics/advantages of the off-axis method:Narrow beam with peak energy at maximum of νμ νeoscillation (∼600MeV).CCQE sample enhanced: high energy tails of the beam reduced(background from non-QE and NC to oscillation signalreduced).Dependence of Eν from Eπ reduced.

The Far Detector: SKMuon neutrino event(νμ μ clear single ring)Electron neutrino event(νe e EM shower, fuzzy ring)20Water Cherenkov detector.1 km deep underground.Cylindrical shape with 39 m ∅and 42 m height.Filled with 50 kton of pure water(fiducial volume 22.5 kton).PMTs: 11.146 in the inner region.Cherenkov photons reach PMTsand produce ring-shaped hit patternUsing the timing and chargeinformation, the interaction vertex,ring direction and flavor of incomingparticle (from the sharpness of edgeof ring) are determined.

21The Near Detectors I:INGRID(ON Axis)ProtonmoduleINGRID (Interactive Neutrino GRID) monitors directly theneutrino beam direction and intensity by means of neutrinointeractions in iron. The beam stability on a day-by-day basis isstudied in this way.INGRID consists of14 on-axis modules (horizontal+vertical) forming a cross.2 extra off-axis modules used to study the axial symmetryof the beam.Each module (7 ton) is composed of 9 iron plates + 11scintillator layers in a sandwich (10mx10m).An extra module, Proton Module, without iron plates isadded in order to detect muons together with protonsproduced by the neutrino beam.

22The Near Detectors II:ND280(OFF Axis)ND280 goal is to measure the flux, energyspectrum and νe contamination beforeoscillation.General purpose to measure: CCνμevents, used for flux normalization andspectrum prediction for the oscillationanalysis and detailed cross section studies;and CCνe events, background to νeappearance.ND280 Magnet & SMRDND280 is built inside the old CERN UA1/NOMAD magnet that provides a dipole magneticfield of 0.2 T.SMRD (Side Muon Range Detector) consistsof 440 scintillator modules inserted in the airgaps of the magnet. It records muons escapingwith high angles, triggers on cosmic ray muonsand helps identifying interactions in thesurrounding cavity.ECAL3 different types depending on the position:DSEcal, BarrelEcal, P0DEcal.These modules are electromagneticcalorimeters using layers of plastic scintillator. Itsrole is to detect photons complementing theinner detectors in full event reconstruction. Theinformation provided by the Ecals is relevant forparticle identification and key in the pi0reconstruction.

The Near Detectors II:ND280(OFF Axis) IIPi 0 detector (P∅D)Tracker3 Time Projection Chambers (TPCs)- MicroMegas detectors. Tracking devices. Theyreconstruct momentum and charge of particles. (Seenext talk: “Calibration and Performance of the T2K TPCs” by<strong>Lorena</strong> <strong>Escudero</strong>).2 Fine Grained Detectors (FGDs)- Thin, wide planes of scintillator bars.- Active target for neutrino interactions: carbon +water (only in the second FGD).- Charged particle tracking.23Scintillator + water detectorOptimized for γ detection and π0reconstruction (neutrino NC process)Water can be subtracted.Study of water cross section.

Mix of FeaturesNeutrino Interaction Event RatesTPC: negligible.INGRID: 1.5 evts/10 14 POTFGD: from the plot:1529 evts in 2.88x10 19 POTevent rate = 5.3evts/10 16 POTNEUTalso...P0D:SK: Predicted from MC models24

Mix of FeaturesDimensionsTPC (Active): 1,8 m (X) x 2,1 m (Y) x 0.772 m (Z)FGD (Active): 1,864 m (X) x 1,864 m (Y) x 0,33 m(Z)TPCResolutionsMomentum resolutionSpatial resolutionTPC PID25

Data Sets26

272010 νμ Disappearance AnalysisEvent ReductionUncertaintiesCut1: Timing

2010 νμ Disappearance Analysis28

Phys. Rev. Lett. 107,041801 (2011)2010 νe Appearance AnalysisPredicted flux-Pion production in (p,θ) bins is based on the NA61 experiment (CERN)measurements, typically with 5-10% uncertainties.-Pions produced outside the experimentally measured phase space, aswell as kaons, are modeled using FLUKA (MC).-Systematic uncertainties of 50% assigned for pions.-Systematic uncertainties for kaons of 15-100% from comparison withdata from:T. Eichen et al., Nucl. Phys. B 44, 333 (1972)-GEANT3 and GCALOR for hadronic interactions to handle particlepropagation through magnetic horns, target hall, decay volume and beamdump.Beam profileFC in SKThe neutrino beamprofile and itsabsolute rate (1.5evts/10^14 POT) asmeasured b INGRIDwere stable andconsistent withexpectations.29An event is categorizedas FC if the maximumnumber ofphotoelectrons on asingle PMT at the exitdirection of the mostenergetic particle isless than 200.

Phys. Rev. Lett. 107,041801 (2011)2010 νe Appearance AnalysisResults based on two physics runs Run1 (Jan.-Jun. 2010)and RunII (Nov.-Mar. 2011).Total 1.43x10^20 POT (protons on target).Sample of CCQE events enhanced.Main backgrounds:Intrinsic νe contamination in the beam.NC π0 events.Observed number of events compared to signal andbackground expectations based on neutrino flux and crosssectionpredictions, corrected with near detector info.Oscillation AnalysisSelect CC νe candidatesCompute withoutoscillations.Normalization with ND280 ratio:Compare withoscillation parameters.to evaluate1.- Predicted flux 2.- ND280 RatioFluxes computed starting from modelsand tuning them to experimental data.Data sample from Run130NEUT MC(GENIE for xcheck)Neutrino interaction in theFGDs entering following TPC(and not in first TPC)90% purity & 38% efficiency(Rs = POT normalized rates of νμ CC interactions)

Phys. Rev. Lett. 107,041801 (2011)2010 νe Appearance Analysis3.- T2K Event Selection1 2 345Cut1 - FC events2 - FCFV events3 - One ring events4 - Electron-like ring events6 7# evtsselectedCut8# evtsselected121 5 - Visible E > 100 MeV 788 specific for6 - No decay electrons (delayed) 641 νe event 7 - Invariant Mass < 105 MeV 6reduction (with forced second ring)88 - Rec. ν E < 1250 MeV631

Phys. Rev. Lett. 107,041801 (2011)2010 νe Appearance AnalysisEvent rates computed incorporating 3-flavor oscillation probabilities and mattereffects with:4.- ExpectedSource NexpBeam νe 0.8νμ NC 0.6νμ CC (νμ νe) 0.1Total 1.5+-0.3Observation exceeds the expectation:Probability to observe 6 events withis 0.7% (2.5 σ significance)5.- RESULTS!Feldman-Cousins unified method:Normal hierarchy, δ=0at 90% C.LBest fit:at 90% C.LBest fit:32Inverse hierarchy, δ=0

Phys. Rev. Lett. 107,041801 (2011)2010 νe Appearance AnalysisUncertaintiesEvent Reduction33

ND280 MeasurementsBackground events for νeappearance are measured at thenear detector ND280:34νe CC eventsNCπ 0 events

2012 Beam Flux PredictionBeam flux is predicted based on:• NA61 π,K measurements• T2K proton beammeasurementsMatrix built with the correlationbetween energy bins for differentneutrino types, detectors.35

2012 Flux + Cross Section Fit36

2012 Cross Section UncertaintiesParameters in the cross section’s models arefitted to ND280 measurementsParametercorrelatedbetweenND280and SK37

382012 Systematic ErrorsContribution from systematic errors to thepredicted number of events (appearance analysis)Numbers arepercentiles (%)

2012 νe Appearance Analysis39

402012 νe Appearance Analysis: FITThree independent analyses done,with consistent results.BACKGROUNDSOne method is based in (p-θ) distribution:• Extended maximum likelihood fit• Data fitted with rate + (pe,θe) shape• Differences in the 2D distribution improve thediscrimination of signal events from background(pe,θe)

The Earthquake41